Removed internal `currentTime` state, relying only on the audio element reported value.
Added `overview_user_seek` event.
Audio element `currentTime` is now updated from both Zoom view and Overview.

- added `zoomview_user_seek` event
- syncing playhead animation if the media element is playing
Partial application of frame nudging.
Better sync with audio seek with the zoom view.

- emitting the `waveform_seek` event on audio element seek instead of emitting it through the API
Merge pull request #22 from bbcrd/fix-seeking

Seeking not working